A jointless artificial foot prosthesis is disclosed by Martin et al. in U.S. Pat. No. 5,897,594. Unlike earlier solutions wherein the artificial foot has a rigid construction provided with a mechanical joint hinge in order to imitate the function of the ankle, the jointless artificial foot of Martin et al. employs a resilient foot insert which is arranged inside a foot molding. The insert is of approximately C-shaped design in longitudinal section, with the opening to the rear, and takes up the prosthesis load with its upper C-limb and via its lower C-limb transmits that load to a leaf spring connected thereto. The leaf spring as seen from the underside is of convex design and extends approximately parallel to the sole region, forward beyond the foot insert into the foot toe-tip region. The Martin et al. invention is based on the object of improving the jointless artificial foot with regard to damping the impact of the heel, the elasticity, the heel-to-toe walking and the lateral stability, in order thus to permit the wearer to walk in a natural manner, the intention being to allow the wearer both to walk normally and also to carry out physical exercise and to play sports. Other similar designs, such as, U.S. Pat. No. 6,077,301; U.S. Pat. No. 6,669,737 B2; and U.S. Pat. No. 6,009,572; and German Patent No DE 299 20 434 U1, have been introduced. Additionally the upper branch of the C-limb is horizontally oriented whereby a prosthetic leg/shank is attached there to. This horizontally oriented upper branch responds to a ground reaction force created in amputee gait by displacing in a proximal and distal direction and not in a substantially anterior/posterior direction. This proximal and distal displacement accomplishes their claimed damping the impact of the heel. The c-shaped foot insert proximal and distal horizontally oriented branches are made rigid with respect to moments. The proximal branch rigidity is derived by a rigid metal coupling element connected to the proximal surface of this branch. This rigid coupling element provides a coupling means for a prosthetic leg/shank element to be coupled thereto. The distal branch rigidity is derived by being attached to a proximal surface of the aforesaid distal leaf spring. The functional deficiency of this design is related to the fact it is a foot insert for an artificial foot wherein the c-shaped spring is configured specifically for a foot. In contrast a human foot is defined as being made up of 25 bones and these bones are distal to a leg/shank. The human leg/shank is a weight bearing longitudinally oriented structure. The human shank is surrounded proximally by muscles wherein these muscles terminate distally as tendons. In gait, these tendons function as mechanical springs. The tendon insertions are located on several of the foot bones. These tendon insertions work in concentration with the human ankle joint to direct closed kinetic chain ankle motion. A prosthetic resilient insert configured for an artificial foot does not include a prosthetic resilient leg/shank element of sufficient length to replicate human calf musculature biomechanical function.
A resilient prosthetic leg/shank which is substantially vertically oriented, which includes a plurality of sagitally oriented struts which are anterior facing convexly curved at their lower ends, whereby they are attached to a prosthetic foot replicates human shank with muscle and ankle function more accurately than a resilient foot insert configured for a prosthetic foot. Therefore, the dynamic response characteristics of these known artificial feet are limited. There is a need for a higher performance prosthetic foot having improved applied mechanics design features which can improve amputee athletic performances involving activities such as running, jumping, sprinting, starting, stopping and cutting, for example.
Other prosthetic feet have been proposed by Van L. Phillips which allegedly provide an amputee with an agility and mobility to engage in a wide variety of activities which were precluded in the past because of the structural limitations and corresponding performances of prior art prostheses. Running, jumping and other activities are allegedly sustained by these known feet which, reportedly, may be utilized in the same manner as the normal foot of the wearer. See U.S. Pat. Nos. 6,071,313; 5,993,488; 5,899,944; 5,800,569; 5,800,568; 5,728,177; 5,728,176; 5,824,112; 5,593,457; 5,514,185; 5,181,932; 4,822,363; 5,217,500; 5,464,441; 5,725,598; and 4,547,913 for example. The dynamic response deficiencies of these known designs relate to leg/shank and foot elements being substantially vertically oriented at their lower end and or utilizing a posterior facing convexly curved ankle area.
Prosthetic design is dynamic, owing, in part, to: the perennial aspiration of creating more comfortable, versatile, or niche products; increased understanding of human anatomy and biomechanics; and recent innovations in designs and materials. One example of recent innovations in design is assignee's anterior facing convexly curved calf shank which has been proven to improve prosthetic dynamics when used in connection with specific foot keel configurations and other components. This anterior facing convexly curved calf shank/leg is disclosed in commonly owned U.S. Pat. Nos. 6,562,075; 7,507,259; 7,429,272; 7,410,503; 7,578,852; and 7,374,578, for example.
However, it is noted that the current existing designs and materials still have significant drawbacks which may be improved upon. More particularly, many existing designs gratuitously incorporate metal or other components which whether individually, or in combination with the overall devices, fail to optimize life expectancy and weight. Metal components are known to wear and lose strength characteristics over time. Furthermore, metal components add to the weight of the prostheses, generally an undesirable characteristic. Other advantageous properties are foregone through emphasis on use of metal components in foot prostheses.
Lighter weight materials provide many advantages when incorporated into prostheses. Carbon fiber, as merely one example, combines a high strength-to-weight ratio with low thermal expansion. Although many prostheses may use a combination of lighter weight materials such as carbon fiber in connection with other metal components, the current art fails to optimize the use of lighter weight materials due to lack of innovation of the underlying design structures compatible with the materials.
One example of how lack of innovation of underlying design structures limits the use of lighter weight materials is evident from the lack of use of the carbon fiber materials in the anterior facing convexly curved and other such calf shank configurations. More specifically, the use of carbon fiber materials to create such shanks and associated foot keels results in inter-laminate shear stresses which split layers of carbon fiber, resulting in partial or complete failure of the resilient component.
Accordingly, there is a lack of innovation with respect to foot prosthetics that would allow for optimization of the use of lighter weight materials, particularly in the shank and foot keel, while maintaining and improving upon other developments and structures in the prosthetic and orthotic industries.